@spprod Thank you for the additional information! Here are next suggestions:
Would there be any logs that you would be able to share from the time you attempt to activate the webhook to see if there are any error messages? Would you also like to try activate the webhook in our nightly build server to see if it reproduces there?
A teammate tested this with links in attachments on webhooks and wasn’t able to reproduce the issue (tried various malformations of the link, formatted as an attachment and formatted as just a post with a link, even tried changing server and client to French).
I know you already mentioned that you verified that the link structure looks correct, but would there be any way for you to post the html of the link or any other way to verify if the link is correctly structured?